1. Field of the Invention
This invention relates to a battery charger suitable for use to charge a battery cartridge to be mounted in a portable telephone terminal, for example.
2. Description of the Related Art
FIGS. 21A and 21B show a general aspect of a conventional portable telephone terminal, battery cartridge to be mounted in the portable telephone terminal, and charging adapter for charging the battery cartridge.
In FIGS. 21A and 21B, the portable telephone terminal 201 has, on its front face, keys 211 for entry of telephone numbers, etc. and a display 212 for displaying a telephone number, dialing memorandum and other information. The portable telephone terminal 201 has an extensile antenna on its top. A battery cartridge 202 can be connected to the back face of the telephone terminal 201.
The battery cartridge 202 contains a secondary battery such as lithium ion battery, for example. As shown in FIG. 21B, the battery cartridge 202 has positive and negative terminals 203A, 203B, and a communication terminal 204. Output from he communication terminal 204 are charge stop information, capacity information, full charge information, battery defect information, and so on.
A charging adapter 205 has formed a hold portion 206 for holding the portable telephone terminal 201 with the battery cartridge 202 set in place. The charge adapter 205 is supplied with power from a power source adapter 207. The charge adapter 205 includes a charging circuit for controlling the charging operation of the battery cartridge 202.
When the battery cartridge 202 is charged, the portable telephone terminal 201 having the battery pack 202 in place is put in the hold portion 206 of the charging adapter 205, and the secondary battery inside the battery cartridge 202 is charged by the charging adapter 205.
The battery cartridge 202 has a display portion 208. Information on the charging status of the battery is shown on the display 208. If the battery is defective, or the charging is stopped by operation of the protection circuit, a warning about the situation is shown on the display 208. Display of such information like the charging control status and caution is based on information from the communication terminal 204 of the battery 202.
More specifically, output from the communication terminal 204 are charge stop information, capacity information, full charge information, battery defect information, and so forth. Charge stop information is output when the protection circuit is activated to stop the charging because of excessive heat generation of the battery, for example. Capacity information is given when the capacity of the battery becomes 70%, for example. Full charge information is generated when the battery is fully charged. Battery defect information is given when the betty is defective. In response to the capacity information or full charge information from the communication terminal 204, the charging state is controlled. Additionally, with the charge stop information or battery defect information from the communication terminal 204, a warning is displayed.
In order to reduce the size and weight of the entirety of the portable telephone terminal, it is important to reduce the size and weight of the battery cartridge 202. However, along with an increase of information output from the communication terminal 204 of the battery cartridge, structure of the battery cartridge 202 inevitably becomes complicated due to complex control signals output from the communication terminal 204, and this makes it difficult to reduce the size and weight or the battery cartridge 202.
That is, in the example shown above, four kinds of information, namely, charge stop information, capacity information, full charge information and battery defect information, are output from the communication terminal 204. Therefore, various control signals enough to make four or more kinds of representations are required to distinguish these four different kinds of information. When control signals are expressed in different numbers of pulses, it is necessary to enable counting and discrimination of four or more different numbers of pulses. If the control signals are expressed in different voltage levels, it is necessary to enable discrimination of four or more different voltage levels. As a result, encoding and decoding processes become complicated, and the circuit size increases. Further, together with complexity of control signals, the possibility of erroneous discrimination of control signals becomes high due to influences from noise, or the like. Therefore, the possibility of operation errors also increases.
It might be possible to provide a microcomputer in the battery cartridge 202 for processing signals from the communication terminal 204. The use of a microcomputer in the battery cartridge 202, however, makes it difficult to reduce the size and weight of the battery cartridge 202. Therefore, it is desirable to make up the entire circuit only with gate circuits without using a microcomputer.
Especially, as the portable telephone terminal, it is strongly desired to contain the charging adapter in the portable telephone terminal 201 and to charge the battery by directly connecting the power source adapter 207 to the portable telephone terminal 201 as shown in FIG. 22. When the charging adapter is built in the portable telephone terminal 201 in this manner, the demand for reducing the size and weight of the charging circuit becomes strong, and it is desired to simplify control signals from the communication terminal.